The present invention relates generally to telecommunication network test equipment. More particularly, the present invention is a Digital Subscriber Line Access Multiplexer (DSLAM) that incorporates built-in subscriber loop and network test and measurement capabilities.
The demand for access to digital communications networks, such as the Internet, is directly related to the speed or rate at which such networks can transfer data. Higher data transfer rates provide a foundation for increased communication efficiency and new types of communication applications or services. These, in turn, fuel demand for more widespread network access and still-higher data transfer rates.
Conventional analog modems currently provide a maximum data transfer rate of 56 kilobits per second (kbps). Other technologies, such as cable modems, can offer significantly improved performance, but typically require changes in a telecommunication network""s underlying architecture. Such changes may necessitate large network infrastructure investments to meet user demand for network accessibility.
Digital Subscriber Line (DSL) technology provides increased communications bandwidth while using existing twisted-pair copper lines that are prevalent throughout much of the world. DSL delivers a basic data transfer rate of 128 kbps. High speed DSL, or HDSL, can deliver a data transfer rate of 1.544 megabits per second (Mbps) in North America, and 2.048 Mbps elsewhere. Asymmetric DSL, or ADSL, can deliver data rates ranging from 1.5 to 9.0 Mbps on a downstream or receiving path, and 16 to 800 kbps on an upstream or sending path. Taken together, varying DSL technologies are referred to as xDSL.
FIG. 1 is a block diagram of a conventional xDSL communications network organization. In FIG. 1, a set of Customer Premises Equipment (CPE) units is coupled to a Main Distribution Frame (MDF). Each CPE unit comprises an xDSL modem, and is located at a customer site. The MDF is coupled to an access matrix, which itself is coupled to a DSL Access Multiplexer (DSLAM) and a test unit. Each of the MDF, the access matrix, the test unit, and the DSLAM reside at an xDSL service provider""s site. The DSLAM is also coupled to a network gateway or hub, which in turn is coupled to a high-speed transmission line or backbone that connects to an external network. Finally, the access matrix, the DSLAM, and the test unit are each coupled to a control computer.
The high-speed backbone is characterized by a data transfer rate much greater than that associated with any given CPE unit. Taken together, the DSLAM, the access matrix, and the MDF provide a signal exchange interface between the high-speed backbone and the CPE units. The DSLAM includes a set of xDSL modems and signal multiplexing circuitry, while the access matrix includes computer-controlled switching circuitry.
Each CPE unit is coupled to the MDF via a network of twisted pair wiring. The signal transfer pathway between any given CPE unit and the MDF is commonly referred to as a xe2x80x9clocal loop.xe2x80x9d A local loop""s maximum data transfer rate is dependent upon its electrical characteristics, as readily understood by those skilled in the art. Due to variations in signal path length, environmental conditions, and interconnection history, any given local loop""s electrical characteristics may significantly differ from those of another local loop. Moreover, a local loop""s electrical characteristics may change over time due to variations in twisted pair line conditions. As a result, the ability to determine accurately local loop electrical characteristics is critical to the installation and maintenance of xDSL connections.
The test unit comprises hardware and software that facilitates local loop electrical characterization. The test unit provides capabilities such as those described in U.S. patent application Ser. No. 09/215,421, entitled xe2x80x9cTelecommunications Transmission Test Set,xe2x80x9d filed on Dec. 18, 1998; and U.S. patent application Ser. No. 09/295,857, entitled xe2x80x9cDetection of Bridge Tap Using Frequency Domain Analysis,xe2x80x9d filed on Apr. 21, 1999.
The organization of the DSLAM, the access matrix, and the test unit as shown in FIG. 1 is undesirably space and cost inefficient. In many prior art configurations, the test unit is roughly comparable in size to the DSLAM itself. What is needed is a different type of configuration that is highly space and cost efficient.
The present invention comprises a Digital Subscriber Line Access Multiplexer (DSLAM) or Concentrator that incorporates built-in hardware and/or software for measuring and/or determining subscriber loop and/or DSL network electrical characteristics. Herein, the present invention is referred to as a Digital Subscriber Line Access and Network Testing Mulitplexer (DSLANTM). In one embodiment, the DSLANTM comprises a set of line cards; a set of xDSL modem cards; a redundant xDSL modem card; a test and switching unit; at least one control unit; and at least one trunk unit. The present invention further comprises an interface unit into which each of the aforementioned elements couples.
The interface unit provides electrical couplings that facilitate selective signal exchange between DSLANTM elements. In one embodiment, the interface unit comprises a midplane circuit board having a first side and a second side. The first side includes electrical connectors for receiving the line cards and each trunk unit, while the second side includes electrical connectors for receiving the xDSL modem cards, the redundant xDSL modem card, and each control unit. Other interface unit embodiments will be readily apparent to those skilled in the art.
The interface unit may include a power bus, a control bus, and a redundancy bus. The power bus facilitates electrical power delivery to each DSLANTM element. The control bus facilitates a control unit""s issuance or assertion of control signals to particular DSLANTM elements, where such control signals may include data signals and memory addresses. Lastly, the redundancy bus facilitates coupling one or more line card ports to the redundant xDSL modem card and/or the test and switching unit, such that the test and switching unit may determine or measure subscriber loop electrical characteristics as further described below.
Each line card, xDSL modem card, and trunk unit is coupled to a control unit. The control unit may comprise a processing unit, a memory, and high-speed switching circuitry. The control unit selectively directs the operation of each DSLANTM element; issues commands to establish particular couplings between and/or within given DSLANTM elements at particular times; and oversees or manages incoming and outgoing data communication traffic.
Each line card is coupled to a Main Distribution Frame (MDF), which in turn is coupled to Customer Premises Equipment (CPE) units associated with subscriber loops. Any given line card provides multiple xDSL communication ports, and includes signal coupling and electrical isolation circuitry. A line card also includes a switch that facilitates coupling line card ports to 1) the redundancy bus; or 2) an xDSL modem card corresponding to the line card in response to a signal, command, or directive received from a control unit. Each xDSL modem card, including the redundant xDSL modem card, comprises conventional xDSL modem hardware and software. Each trunk unit serves as an interface for carrying aggregated data communication traffic between a control unit and a hub, where the hub is coupled to a high-speed network.
The test and switching unit is coupled to the redundancy bus, and comprises power interface circuitry, control logic, a relay matrix, a memory, and a Copper Loop Tester (CLT). The test and switching unit""s control logic serves as an interface for communicating with the DSLANTM""s control unit. The relay matrix comprises a set of switches and a port selector. In response to a signal, command, or directive issued by the control unit, the relay matrix may route signals present upon the redundancy bus to the redundant xDSL modem card and/or the CLT. The port selector chooses a given line card port present upon the redundancy bus for coupling to the CLT, in accordance with a control unit signal, command, or directive. Thus, via a line card""s switch, the redundancy bus, and the relay matrix, the CLT may be coupled to 1) an isolated subscriber loop, or 2) a subscriber loop that may communicate or exchange signals with the redundant xDSL modem card.
The CLT comprises a subscriber loop test and measurement unit, and in one embodiment includes a processing unit, a Digital Signal Processor (DSP), a memory, and a set of test units. The test units may include a Digital Multimeter (DMM) test circuit, a Time Domain Reflectometry (TDR) test circuit, a line impairment test circuit, and/or other test circuits. In one embodiment, the CLT is essentially or generally analogous in structure and functionality to subscriber loop test equipment described in U.S. patent application Ser. No. 09/215,421, entitled xe2x80x9cTelecommunications Transmission Test Set,xe2x80x9d filed on Dec. 18, 1998; and 2) U.S. patent application Ser. No. 09/295,857, entitled xe2x80x9cDetection of Bridge Tap Using Frequency Domain Analysis,xe2x80x9d filed on Apr. 21, 1999.
In response to commands issued by the control unit, the CLT performs tests to measure and/or determine one or more subscriber loop electrical characteristics. In one embodiment, the CLT stores test results to the control unit via the test and switching unit""s memory. The control unit may subsequently retrieve such test results. In one embodiment, the test and switching unit includes a direct CLT control port, through which a device external to the DSLANTM may direct CLT operation and receive or retrieve test results.
As the present invention comprises a single device having line card port routing, port selection, and CLT elements incorporated therein, the present invention provides a highly compact, cost efficient DSLAM capable of electrically characterizing subscriber loops.